Cardiac function management systems are used to treat arrhythmias and other abnormal heart conditions. Such systems generally include cardiac leads, which are implanted in or about the heart, for delivering an electrical pulse to the cardiac muscle, for sensing electrical signals produced in the cardiac muscle, or for both delivering and sensing. The lead typically consists of a flexible conductor that may define a central channel or lumen, surrounded by an insulating tube or sheath extending from a connector pin at the proximal end to one or more electrodes along the lead body at the distal end.
Cardiac lead placement may be accomplished by introducing the lead through a major blood vessel and advancing a distal end of the lead to a final destination in or near the heart. For example, for some therapies such as cardiac resynchronization therapy (CRT), the distal end of the lead is advanced through the coronary sinus and coronary veins to the epicardial surface of the heart. To stimulate cardiac tissue, the electrodes should be arranged to contact the myocardial side of the vessel at the final destination. Some leads include a pre-shaped curved or helical portion that forces the electrodes along the lead body against the vessel wall. However, since the orientation of the curved or helical portion of the lead is difficult to predict or control, the likelihood of the electrodes contacting the myocardial side of the vessel is low. One approach to increasing the likelihood of electrode contact is to increase the number of electrodes along the curved or helical portion. However, this increases the complexity of the lead, and the number of electrodes may be limited by available connections to the pulse generator. Another approach to increasing the likelihood of electrode contact is to increase the length of individual electrodes. However, the added electrode length could affect the ability of the distal end of the lead body to retain its curved or helical shape.